With the introduction of the "Passengers" tag, this new compound holds a copy of the entity the player is currently riding. "AttachLeast" and "AttachMost" are the UUIDLeast and UUIDMost of that entity, while "Entity" holds the actual data.

Essentially the only use for "DataVersion" for map-makers is to unsure the player is playing in the correct version. For example, the value for version 1.10.2 is 512; the following commands would notify the player that the map was made for 1.10.2 if they do not have the required tag: